Added a note to use sbt 0.13.9 and remove unnecessary sonata repository
from the instructions.
Finally removed a link to a non existent page and added a link to
ensime-sbt GitHub page for further instructions.
Helm seems to treat "!" specially in pattern matching, so having a ! in
the pattern string when traversing directories is problematic. This
change fixes#2737, because as far as I can tell "+" has no special
meaning in a helm pattern.
Of course, we can choose a different character, but I'm fond of "+" as
representing "more layers here".
